check type of attribute keys

[malmans2]

Closes #1037
This PR adds a check that does not allow to use attribute keys other than strings.

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[codecov]

Codecov Report

Merging #1066 (879eca2) into main (dcc6ded) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1066   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          34       34           
  Lines       13846    13865   +19     
=======================================
+ Hits        13839    13858   +19     
  Misses          7        7           

Impacted Files	Coverage Δ
zarr/attrs.py	100.00% <100.00%> (ø)
zarr/tests/test_attrs.py	100.00% <100.00%> (ø)

[malmans2]

I'm not sure whether we should add a note somewhere in the documentation/docstrings. Other than that, this PR is ready for review.

cc:
@joshmoore

[joshmoore]

@malmans2 : I don't think I can update your branch with the latest origin/main. Could you do so to get all the tests passing?

[malmans2]

@malmans2 : I don't think I can update your branch with the latest origin/main. Could you do so to get all the tests passing?

Done! Let me know if we should start a deprecation cycle.

[joshmoore]

Happy if someone who wants to be adventurous speaks up, but I'd err on the side of the deprecation cycle.

[joshmoore]

Sorry for the delay, @malmans2, and thanks for the deprecation cycle. If we're temporarily accepting the stringification, would you be able to workaround your TypeError by explicitly calling str()?

[joshmoore]

Thanks, @malmans2! Rolling into 2.13